If you have ever referred to the ASTM (American Society for Testing and Materials) standard documents used for steel design and construction, you’ll notice that ASTM A53 steel pipe designations are different than ASTM A500 round hollow structural sections and they are manufactured to meet different standards. While ASTM A500 is available in cross-sections matching each of the cross-sections for ASTM A53 steel pipe, there are many more cross-sections available in A500.

In this article, I will outline the differences between A500 structural hollow sections and A53 pipe and discuss why ASTM A500 is the better choice.

ASTM A53 Pipe

ASTM A53 pipe, a standard specification for black and hot-dipped, zinc-coated, welded and seamless steel pipe, is used for mechanical and pressure applications as well as ordinary uses in steam, water, gas and air lines. ASTM A53 can be formed and welded. Pipe sizes are properly designated using the Nominal Pipe Size (NPS). This is the nominal pipe diameter with a scheduled wall thickness (i.e., 4 inch Schedule 40 pipe).

ASTM A500 Pipe

ASTM A500 is a standard specification for cold-formed welded and seamless carbon steel structural tubing in round, square and rectangular shapes. ASTM A500 is the most common specification in North America for Hollow Structural Sections. Round HSS sections are properly designated by indicating the outside diameter in decimal inches by the nominal wall thickness to three decimal places (i.e., 5.563 x 0.250).

Why A500?

Since ASTM A500 is a structural specification, round HSS produced to this specification are fit for purpose when used for structural applications and general construction use. ASTM A53 is a pipe specification and is intended to be used in mechanical and pressure applications.

The specified yield strength of A500 Grade C (the most commonly available grade) is 46 ksi. The specified yield strength of A53 Grade B is 35 ksi. That’s over a 30% increase in yield strength. Therefore, A500 round HSS have greater strength-to-weight ratios than A53 pipes. So, with round HSS you need less steel, by weight, to do the job—less weight equals less cost.

The tolerances of A500 are tighter than those of A53, therefore the A500 round HSS have a higher degree of quality and less variability.

Round HSS have a superior surface finish and do not come with the lacquer coating that typically comes on A53 pipe. This saves money and time as this lacquer coating needs to be removed from the A53 pipe to accommodate welding and painting.

A53 pipe are only available in standard pipe sizes. Round HSS come in a variety of sizes and wall thicknesses.

Lastly, the ASTM A53 Specification requires testing (i.e., pressure testing) that is not needed for structural applications. This additional testing can add unnecessary additional cost.

ASTM A500 applications include structural supports, building columns, highway signs, oil field services and communication towers, to name a few. All steel structures have their pros and cons, but ultimately ASTM A500 is the better choice when you need a round profile.

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